1. Field of the Invention
The present invention relates to external fixator systems useful in the repair of bone fractures, in limb lengthening, and in the correction of bone deformities. Even more particularly, the present invention relates to an improved external fixator system, useful with the so called "Ilizarov" method that uses rings held apart by threaded rods and threaded fasteners and wire rod components, used in the fixation of fractures, limb lengthening, and the correction of bone deformities wherein an improved ring construction that affords radiolucency is comprised of a composite plastic-carbon fiber material having lightweight, high strength, high modulus characteristics.
2. General Background
The repair of traumatized bone can be accomplished by the use of an external fixator device which includes a number of curved rings or curved half rings that are attached and spaced apart but structurally connected using a plurality of tie rods. These tie rods are simply inserted through one of several holes formed in each of the selected half rings or rings at a desired circumferential position and affixed thereto by bolting. Several rings and several tie rods can be used by the surgeon in order to create an overall frame about the patient's arm or leg. Transversely extending pins or wires attach to these rings and then extend transversely from the rings into the bones, so that the frame and transverse pins support and/or load the bone tissue in a desired manner.
This system is generally referred to in the art as the "Ilizarov" method and can be used for the purpose of external fixation of heavily damaged or heavily traumatized bone. The "Ilizarov" method can also be used for lengthening various congenital and acquired shortenings and other defects of skeletal segments wherein the rings and tie rods form part of compression-distraction apparatus.
The "Ilizarov" method is described generally in the Oct. 8, 1989 issue of Parade Magazine in an article entitled "Stretching The Body's Power To Grow", and in U.S. Pat. No. 4,615,338, issued to Gavril A. Ilizarov et al. The '338 Pat., entitled "Automatic Compression-Distraction Apparatus", is directed to an improved compression distraction apparatus. The '338 Ilizarov patent references earlier prior art publications of the same inventor, including USSR Inventor Certificate No. 848,011, cl.A 61 B 17/18, also published in the Bulletin of Inventions No. 27,1981. A second prior art disclosure relating to a drive of a compression distraction apparatus appears in USSR Inventor Certificate No. 865,284, cl.A 61 B 17/18, published in the Bulletin of Inventions No. 35,1981. These prior Ilizarov publications all relate generally to the Ilizarov external fixation system which uses metal rings, threaded rods, threaded fasteners, and other metallic components in the fixation of fractures, limb lengthening and the correction of bone deformities. Other attempts have been made to improve the "Ilizarov" method by modifying the ring and half-ring construction. A circular ring was developed by Kronner which used random carbon fiber reinforced nylon. This particular composite had a reported disadvantage of an inability to hold pins securely.
Fixano manufactured a device sold by Danek in the U.S. which used carbon fiber reinforced plastic half rings.
U.S. Pat. No. 3,977,397 discloses a liner impregnated phenolic ring of circular cross section.
Other patents relating to the Ilizarov system include the Koeneman et al. patents, U.S. Pat. Nos. 4,757,809 and 4,747,400. In the '400 Pat., the frame has side rails, each with a polyamide foam core, wrapped with a composite of graphite or glass fibers impregnated with thermo-plastic or thermo-setting resin.
European patent EP 87112273 and U.S. Pat. No. 4,604,996 issued to W. Herzberg discuss the use of glass fibre reinforced hoses and connections which can be filled with self-curing plastics, wherein such external fixture can be produced at low cost and offers no obstruction to x-rays.
The Mears patent, U.S. Pat. No. 4,620,533, relates to an apparatus for externally fixing bone fractures with clamps having universal ball joints to pins and a rigid bar. The bar is preferably of epoxy/carbon or epoxy/fiberglass composite, and the clamps are of nylon/carbon fiber composite, both being x-ray translucent.
The metallic nature of the Ilizarov system has presented clinical difficulties in the evaluation of patient's radiographs, because of the high radiopacity of the metallic parts. One of the most common problems incurred is that the surveillance of bone healing or bone distraction is impeded by radiographic shadowing resulting from the metallic components used in the Ilizarov system. Secondarily, the fully assembled Ilizarov frame can constitute a significant added weight which can be problematic in pediatric and upper extremity cases.
Prior attempts to solve this problem have not been able to supply the desirable physical and load carrying characteristics of the present invention including light weight, high strength, high modulus of elasticity (i.e., near that of steel) and radiolucency.